Why aren't monoracial couples seen as being pretty much the same as "cousin lovers" the same as b/w biracials are?

I was talking to a Dominican woman on here about this, and even she thought it was weird that a lot of us [black/white biracials] get the stigma as "looking related" as a couple but not the average monoracial couple.. Wouldn't that also make two blonde hair, blue eye Swedes cousin lovers? Two Somalis together the same?

Also is this a consent theme within the wasian community and the rest of the other mixed community as well? I don't want to just straight up generalize but I've only seen this being said towards anyone that's of afro decent mixed. But t that could just be me.